In modern printworks ever higher processing speeds and capacities are required in connection with the further processing of printed products from rotary presses. This is inter alia due to the fact that modern rotary presses permit, apart from multi-colour printing, high quality offset printing and consequently there is an increase in the number of brochures, magazines and other printworks products which can be produced. Simultaneously processing must have great flexibility, so that the maximum number of final formats of the printed products must be obtainable using the same plant. Significance is also attached to costs, because in flexible plants identical components must be usable for different functions, whilst permitting the very satisfactory use of high capacity partial plants. However, flexibility is also required in connection with the extendability of plants, because often at a later time an existing plant must be usable for larger numbers or for new printed products. There is also a desire for maximum utilization and loading of systems, particularly in view of the relatively high costs for printing presses and conveying systems.
Conventional conveying and processing plants in printworks are all based on serial processing concepts. Printed products or partial products are usually conveyed by means of conveyor belts, conveyors, etc. in a conveying line, often as a scale or stream flow and supplied to processing plants. Since, as a result of their operating principle, rotary presses generally print paper webs in serial form, it is natural to further process the printed products in serial manner. Serial processing is often also necessary due to the working steps during further processing requiring a serial sequence. Therefore up to now conventional conveying and processing plants have had to adhere to this serial principle.
For special applications, particularly when high processing capacities are desired, serial processing plants are adapted and precautions taken leading to a certain processing capacity increase. However, these precautions have only related to specific bottlenecks in processing and no solution has been provided to the fundamental problem, i.e. increasing the processing capacity and in particular making the overall plant or at least certain working steps therein more flexible. Thus, e.g. buffer plants or means have been provided, or by using sorting gates the printed product flow has been subdivided into several partial flows. Such an apparatus is e.g. described in U.S. Pat. No. 4,866,910, Reist. This invention discloses a method and an apparatus in which one or more continuous flows of printwork products is subdivided onto the feed segments of at least two processing stations without using buffer means. Another method according to U.S. Pat. No. 4,402,496, Muller shows how a conveyor is subdivided into several paths, "so as to be able to make it possible to use the known and proven conveying technology". The problem to be solved is to maintain the feeder capacity, whilst retaining the aforementioned conveying technology.
However, it has been found that the "known and proven" serial conveying concepts suffer from significant disadvantages, which are particularly prominent in the case of large conveying capacities. As in all serial processes, bottlenecks necessarily occur at points having a longer passage time or a slower clock cycle, which is also due to inadequate flexibility. As stated hereinbefore, the problems of such a bottleneck can be partly solved with a buffer. However, if the flow must pass through a bottleneck for a long period or even permanently without any interruption, it is necessary that a fundamentally unlimited buffer capacity must be provided. Therefore all the following plants can only be operated at the bottleneck capacity. Obviously in such cases the conventionally used buffering constitutes an inadequate solution, if a high overall system capacity is sought. Therefore other known solutions, similar to the apparatus according to U.S. Pat. No. 4,402,496, have attempted to get round the bottleneck to a limited extent, in that the requisite processing capacity is divided up over several conveying or processing paths. Several fundamentally independent processing paths are created, which in turn use serial conveying. If e.g. a following processing is to be carried out with a work station which has a very high capacity, the separate following paths must be rejoined, which requires the use of complicated means. However, the subdivision of the conveying paths also suffers from the disadvantage that, apart from a large space requirement for the separated paths, each of said paths has its own control system, own processing means, etc. Thus, in actual fact the mechanical and organizational expenditure is increased. As a rule when subdividing the main conveying path the following paths are alternately fed through the sorting gates. Thus, for a short time, i.e. during the loading time from the main conveying path, each of the following paths must be able to assume the high conveying capacity of the main conveying path. Therefore the individual following paths must be designed for an equally high capacity, although this is only required for a short time, or buffers must be additionally used. With very high capacities, i.e. when processing 80,000 or more items per hour, conventional plants with serial conveying, which solve capacity problems with following paths, are confronted with fundamental problems, because the physical processing limits are reached.